The present invention relates to a latch needle for a textile machine, including a latch which is pivotal in a longitudinal slot of a needle shank and which is pivotally mounted on two coaxial shaft stubs by means of a continuous bearing bore. The shaft stubs are disposed at needle shank cheeks which laterally delimit the longitudinal slot, with the shaft stubs projecting into the longitudinal slot. The invention also relates to a method of producing such a latch needle.
Latch needles of this type are widely used in various textile machines, particularly in knitting machines, and also, for example, in special sewing machines. Such latch needles in practice have two shaft stubs which project laterally into the longitudinal slot and which are formed by parts which are pressed out of two needle shank checks and deformed into the latch hole in the manner of bearing pins that are formed in one piece on the needle shank cheeks. Examples of latch needles with this type of latch bearing are disclosed, for example, in U.S. Pat. No. 3,934,109 and British Pat. No. 836,297.
Due to the fact that the two bearing pins have no firm connection with one another and contact one another in the latch bore at most with their frontal faces, the latch bearing has a certain amount of elasticity which has been found to be favorable with a view toward reducing the occurrence of breaks in the needle shank cheeks. It has been found in practice, however, that the material of the lateral cheeks displaced into the latch bore, due to its unpredictable flow behavior, is able to only incompletely adapt its shape to the shape of the latch bore so that in fact more or less great deviations result from the theoretical cylindrical shape of the shank stubs. It is a fact that even in a latch needle just received from the factory, the load per unit of surface area of the latch bore on the bearing pin which has been shaped through this bore at the needle shank cheeks in an embossing process is relatively small. With increasing periods of operation, a danger of needle malfunction arises from the fact that, as a result of the wear occurring on the latch bearing surface area the latch bearing play on the two bearing pins, whose shape only very imperfectly corresponds to a cylindrical shape, increases to such an extent that the free end of the latch, during the closing movement of the latch, misses the needle hook or slides off of it on the side, thus making the needle unusable.
U.S. Pat. No. 3,934,109, discloses a measure directed toward this problem which includes welding together, for example, by means of a highly focused laser beam, the frontal faces of the punched bearing pins which form the shaft stubs from material shaped from the shank cheeks. However, this measure has not overcome the problem. Such problem becomes more significant if the latch needles are used in fast moving knitting machines or are used to knit robust yarns, i.e. the latch bearing must meet very high demands, not only with respect to the accuracy of the latch guidance but also with respect to mechanical strength.
Other latch needles are known, for example, from German Pat. No. 1,296,734, in which the latch bearing is formed by a one-piece, cylindrical shaft pin or bolt which traverses the longitudinal slot of the needle shank and rests with both its ends in corresponding coaxial bores of the shank cheeks, it being either screwed to the shaft checks or rigidly connected therewith by means of laser welding. Although a latch needle, whose latch is mountd on such a separately manufactured, precisely cylindrical, continuous shaft bolt which is inserted into a corresponding transverse bore of the shank cheeks has excellent latch guidance with respect to accuracy and wear resistance due to the precisely worked cylindrical jacket faces of the smooth shaft bolt, such latch needles are today almost without significance because the latch bearing arrangement employing a continuous shaft bolt is rigid and is completely inelastic transversely to the axis of symmetry of the needle. This inevitably causes a break in the needle shank checks when the needle is subjected to high, and particularly to dynamic, stresses, thus limiting the service life of such needles in an undesirable manner.
Additionally, it is known from German Pat. No. 215,749 to mount the shaft bolt on one side in a blind bore of the associated needle shank cheek and to secure it by welding on the other side in the transverse bore of the corresponding needle shank cheek. Although this does provide for a certain amount of elasticity in the latch bearing, such elasticity is limited, aside from the fact that the manufacture of such needles is expensive so that they are not suitable for mass production.